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4. Internal Valving
The flightDAQ2 contains the necessary valving to purge the measurement lines of the flightDAQ2
and to perform a re-zero – even when the measurement lines are subject to pressures.
The schematics below illustrates the function of the internal valves. There are two states of the
scanner shuttle valve – run mode and calibrate mode. The shuttle valve is shifted by applying
pneumatic pressure (from the supply gas port) which is switched by additional internal valves.
In run mode, the measurement ports on the integral SQDC are connected to each measurement
port on the scanner. The reference port is connected to the barometric sensor and the reference
cavity of the differential pressure scanner. In this mode normal differential or absolute pressure
measurements can be performed.
In calibrate or purge mode, the differential pressure transducers are all connected to the calibrate
port and the measurement lines are connected to the purge supply valve. Purge gas supplied to the
purge port on the top of the flightDAQ2 can then be switched (by using the internal valve) to purge
the measurement lines of contaminants and moisture.
Please see note in section 6.7.3 on purge methods for on-ground and in-flight situations.
As all the differential transducers are connected to the calibration port in this mode, it is possible to
re-zero the scanner and remove any zero offset – even when the system is subjected to pressures.
This is simply achieved by externally connecting the calibrate and reference port together (as shown
in the cal / purge mode schematic) which will ensure that the differential transducers have no
pressure differential across them.
All of the internal valves are controlled via the embedded web server or over the communications
protocol used. In addition to manually actuating each valve, we offer a re-zero and purge routine
that will actuate all the necessary valves in the appropriate sequence.
